1. Field of Invention
This invention relates to electrochromic display devices and more particularly relates to electrochromic display devices which are able to display a large amount of information within a limited display area.
2. Prior Art
Image display devices which utilize electrochromic materials (materials which undergo reversable coloration as a result of electrochemical oxidation-reduction reactions) are well known. For example, a display device using inorganic oxide such as tungsten oxide, molybdenum oxide, etc., as the electrochromic material, has been disclosed in U.S. Pat. No. 3,827,784. A display device using organic dies such as viologen, has been disclosed in U.S. Pat. No. 3,806,229.
A greater amount of electrical energy is required in order to drive these electrochromic display devices than is needed to drive liquid crystal display devices. However, since electrochromic display devices have a memory effect, an image once displayed will persist without further energy consumption. Accordingly, the mean energy consumed is approximately equivalent to that consumed in driving liquid crystal display devices. Furthermore, since the display contrast in electrochromic display devices does not depend upon the glancing angle, legibility is very good. Accordingly, electrochromic display devices are appropriate for use in display devices and electronic timepieces, desk top calculators, hand held calculators, etc.
Electronic timepieces using electrochromic display devices have been disclosed in U.S. Pat. Nos. 3,839,859 and 3,950,936. In these electronic timepieces, display electrodes consisting of a large number of segments are selectively driven and numerals are displayed by combining colored segments.
In these electrochromic display devices, however, display electrodes are installed on only one-half of a pair of substrates that constitute the display cell. A counter electrode is installed on the remaining substrate. Accordingly, the number of segments that can be installed is of a limited number and it is not possible to overlap or cross segements. Therefore, the types or variations in the patterns that can be displayed is limited. Furthermore, the character forms of numerals, letters, etc., are unnatural patterns with poor legibility.